Dr. Mercola

Sleep is such an important part of your overall health that no amount of healthful food and exercise can counteract the ill effects of poor sleeping habits.

Researchers have linked poor sleep to a number of ailments, from short-term memory loss and behavioral problems, to weight gain, diabetes, and even increased risk of cancer, just to mention a few.

Yet while most of the literature emphasizes the ramifications of insufficient sleep, research shows too much sleep isn’t good either.1 Studies have linked excessive sleep to health risks ranging from depression to an increased risk for stroke, just to name a few.

There is, it appears, a “Goldilocks zone” when it comes to sleep.

After reviewing more than 300 studies to ascertain how many hours of sleep most people need to maintain good health, the panel of experts concluded that most adults need seven to nine hours, or right around eight hours, of sleep each night.

Studies suggest consistently sleeping less than eight hours, and more than nine — with the exception of children and teens — is associated with health risks. (To see the sleep recommendations for all age categories, please see my previous article, How Much Sleep Is "Enough"?)

Sleeping More Than Eight Hours May Increase Stroke Risk in Seniors

According to one of the most recent analyses,2 seniors who regularly slept more than eight hours per night had a 46 percent increased risk of stroke compared to those who slept between six and eight hours per night.

Interestingly, those whose sleep pattern changed over the nearly decade-long study, going from sleeping less than six hours to sleeping for more than eight hours per night, had about four times higher risk of stroke compared to those whose sleep remained consistently average throughout.

The cause for these findings, however, is still unclear. As reported by CBS News:3

“[T]he researchers don’t know if the long sleep is a cause, consequence, or early warning sign of declining brain health. After reviewing previous research on the possible link between sleep and stroke risk, they said they only found an association that they can’t explain.”

The answer is not to cut sleep, as getting inadequate sleep can have serious health consequences. However, if you notice that you need more sleep than normal, you’d be wise to evaluate your lifestyle, and make some healthy changes there.

Most researchers agree that excessive sleep tends to indicate an underlying health condition.

Dr. Alberto Ramos, who wrote an accompanying editorial to this study suggests long sleepers (i.e. those who sleep more than nine hours a night) would be wise to “monitor their lifestyle, eating a healthy diet and exercising regularly,” adding that:

“Adults over the age of 60 or 65 who notice they are sleeping more should make sure their cardiovascular risk factors such as blood pressure and cholesterol are under control.”

Seven Health Risks Associated with Sleeping Too Much

Besides suggesting that you may be at an increased risk for stroke, consistently logging more than nine hours has been associated with a number of other health hazards as well, including the following:4,5

Depression

A genetic study6,7 involving adult twins found those who slept between seven and nine hours per night had a 27 percent “total heritability” of depressive symptoms.

Among those who slept 10 hours per night, the genetic influence on depressive symptoms rose to 49 percent. According to the authors:

Other research conducted by the U.S. Centers for Disease Control and Prevention found that long sleepers reported mental distress more frequently than those getting a normal amount of sleep.

Diabetes

Sleep deprivation can quickly impair your insulin sensitivity and lead to insulin resistance — a precursor to type 2 diabetes.

But too much sleep can have a similar impact.

One Canadian study8 found that those who slept more than eight hours a night were twice as likely to develop type 2 diabetes over the next six years, compared to those who slept between seven and eight hours.

Weight gain

Weight gain is another health consequence typically associated with lack of sleep, but excessive sleep can wreak similar havoc.

In the Canadian study mentioned above, those who slept 10 hours a night were 25 percent more likely to gain 5 kilos (kg) over the course of six years compared to those who slept less.

According to the authors, the results “emphasize the need to add sleep duration to the panel of determinants that contribute to weight gain and obesity.”

Heart problems

Heart problems such as angina (chest pain associated with heart disease) are also associated with excessively long sleep cycles.

For example, one study9 found that sleeping for more than eight hours a night doubled the risk of angina.

Memory loss and declined brain function

A 14-year long study involving women found that long sleepers suffered more rapid brain aging.

Overall, they were mentally two years “older” compared to those who got seven to eight hours per night.

Another study10 found similar results. Here, men and women in their 60s and 70s who slept nine hours or more each night had a more rapid decline in their cognitive function than those who sleep between six and eight hours.

While scores of cognitive function declined across the board, regardless of how much or little sleep they got over the three-year study, the long sleepers (nine or more hrs./night) had nearly double the amount of cognitive decline as the normal sleepers six to eight hrs./night).

This decline is often seen in mild cognitive impairment, which is a risk factor for dementia.

While the cause is undetermined, one theory is that it has to do with fluctuating neurotransmitter levels.

Premature death

A meta-analysis of 16 different studies involving nearly 1.4 million study participants found that both long and short sleepers had an increased risk of dying, from any cause.

Sleeping more than eight hours was associated with a 1.3 times greater risk of all-cause mortality.

Daylight Helps Anchor Your Circadian Rhythms

While it may not be immediately obvious as to why, light is actually a crucial component of sleep. I highly recommend listening to biomedical science researcher Rhonda Patrick’s hour-long interview with Dan Pardi above to learn more about this. Pardi does research work with the Behavioral Sciences Department at Stanford University and the Departments of Neurology and Endocrinology at Leiden University in the Netherlands.

In this interview, he explains the circadian rhythm of sleep, and how it impacts your health, brain detoxification, memory, obesity, and more — and the role of light.

One of the reasons why so many people struggle with poor sleep is due to the prevalence of unnatural lighting environments. When you spend the majority of your day in a windowless office and your evenings in rooms bathed in artificial light, your brain struggles to determine what time it is. Sleep dysfunctions such as insomnia can easily result.

The reason why natural sunlight is so important is because it serves as the major synchronizer of the master clock inside your brain — a group of cells called the suprachiasmatic nuclei (SCN). As a group, these nuclei synchronize to the light-dark cycle of your environment when light enters your eye. You also have other biological clocks throughout your body, which are synchronized to this master clock.

So synchronization is taking place on two levels. First, your master clock synchronizes to your environment, and then your body synchronizes with your master clock.

In terms of practical advice to help you maintain healthy master clock timing, you want to get bright light exposure during the day. Many indoor environments simply aren't intense enough to do the job well. So-called "anchor light" anchors your rhythm, causing it to be less fragile, so that light at night has less of an ability to shift your rhythm.

As for how much light exposure you need, Pardi says the first 30 to 60 minutes of outdoor light exposure creates about 80 percent of the anchoring effect. This means that even just going outside for half an hour at lunch time can provide you with the majority of anchoring light you need to maintain a healthy circadian rhythm. The ideal time to go outdoors is right around solar noon but any time during daylight hours is useful.

Artificial Lighting Desynchronizes Your Biological Clocks

In the non-artificial light environment of our historical past, people experienced greater light exposure during the day, between sunrise and sunset, than most people do today. With the advent of artificial lights and lighted electronic gadgets such as TVs and computers, we are now exposed to a lot more light over any given 24-hour period, and a lot less darkness, than our forebears.

In terms of light intensity, outdoor light is far more intense than indoor light. Light intensity is measured in lux units, and on any given day, the outdoor lux units will be around 100,000 at noon. Indoors, the typical average is somewhere between 100 to 2,000 lux units — basically two orders of magnitude less.

The combination of light deficiency during the day and excessive light exposure at night creates a very novel situation for your internal time keeping and biological pace setting mechanisms, causing your biological clocks to get out of sync.

The consequences of asynchronized or mistimed (out-of-sync) circadian rhythms include alterations in physiological and cellular functions, behavior, cognition, and mood. Shift workers, for example, are known to have four- to five-folds higher rates of cancer than the average population. They also have higher rates of obesity and diabetes.

But you don’t have to be a classic shift worker to increase your risk for these conditions. Simply being indoors all day and working on your computer or watching TV late into the evening can cause similar disruptions in your circadian rhythms.

Avoid Light Exposure Before Bedtime

The hormone melatonin acts as a marker for biological timing, meaning it influences what time of day or night your body thinks it is, regardless of what time the clock says. As darkness sets in, and less light hits your eyes, your melatonin production increases. In addition to making you feel mildly sleepy, its primary function is to message all the biological clocks synchronizing to your master clock that “it is now nighttime; start performing nighttime activities.”

While some activities are shut down, others are activated.

As mentioned in the featured interview, melatonin also controls over 500 genes — including genes involved in angiogenesis, the process of growing blood vessels to feed tumor growth — so it’s very important for health and basic biological functioning, and it’s entirely regulated by environmental light conditions. This really tells us something about the importance of living as closely in tune with the environmental cycle of day and night as possible.

Somewhere between 50 to 1,000 lux is the activation range within which light will begin to suppress melatonin production, which instructs the biological clocks to perform daytime activities and maintain wakefulness. Were you to live in the wilderness without artificial lighting, you’d automatically get progressively sleepier as soon as the sun sets, and would wake with the rise of the sun.

Since melatonin is a regulator of your sleep cycle, when it is suppressed, there is less stimulation to promote sleepiness at a healthy bedtime. This contributes to people staying up later and missing valuable sleep. One 2011 study11 compared daily melatonin profiles in individuals staying in room light (<200 lux) versus dim light (<3 lux).

Results showed that, compared with dim light, exposure to room light before bedtime suppressed melatonin in 99 percent of individuals, and shortened the time period when the body has an elevated melatonin level by about 90 minutes.

That’s an hour and a half of tossing and turning in bed, unable to fall asleep. The authors concluded that:“[C]hronically exposing oneself to electrical lighting in the late evening disrupts melatonin signaling and could therefore potentially impact sleep, thermoregulation, blood pressure, and glucose homeostasis."

How to Support Your Circadian Rhythm and Sleep Better for Optimal Health

Even minor adjustments to your daily routine and sleeping area can go a long way to ensure uninterrupted, restful sleep and, thereby, better health. I suggest you read through my full set of 33 healthy sleep guidelines for all of the details, but to start, consider implementing the following changes to ensure more high quality shut-eye:

Avoid watching TV or using your computer in the evening, at least an hour or so before going to bed

These devices emit blue light, which tricks your brain into thinking it's still daytime. Normally, your brain starts secreting melatonin between 9 and 10 pm, and these devices emit light that may stifle that process.

You can also download a free application called F.lux that automatically dims your monitor or screens in the evening, which can help lessen the adverse effects if you have to use them in the evening.

Get some sun in the morning, and at least 30 minutes of BRIGHT sun exposure mid-day

Your circadian system needs bright light to reset itself.

Ten to 15 minutes of morning sunlight will send a strong message to your internal clock that day has arrived, making it less likely to be confused by weaker light signals during the night.

Also, if you work indoors, make a point to get outdoors for at least a total of 30 to 60 minutes during the brightest portion of the day.

Sleep in a dark room

Even the slightest bit of light in your bedroom can disrupt your body’s clock and your pineal gland's melatonin production. I recommend covering your windows with drapes or blackout shades, or using an eye mask.

Install a low-wattage yellow, orange, or red light bulb if you need a source of light for navigation at night

Light in these bandwidths does not shut down melatonin production in the way that white and blue bandwidth light does. Salt lamps are handy for this purpose.

This increases your core body temperature, and when you get out of the bath it abruptly drops, signaling your body that you are ready to sleep.

Avoid electromagnetic fields (EMFs) in your bedroom

EMFs can disrupt your pineal gland and its melatonin production, and may have other negative biological effects as well. A gauss meter is required if you want to measure EMF levels in various areas of your home.

Ideally, turn off your wireless router while sleeping.

Use a fitness tracker to track your sleep

Chances are you’re not getting nearly as much sleep as you think, and using a fitness tracker that monitors your sleep can be a useful tool to help motivate you to get to bed earlier so you can get eight hours of sleep.

Part of the equation too is going to bed earlier, as most of us have to get up at a preset time.